Hate to me-too, but me-too this issue. I've tried every variation of double-tap ctrl/alt keys, single-tap, nothing works. Instant send is a key part of Launchbar - I've almost stopped using it since this broke. I tried @martenzi's tips but to no avail.
And 2nding @strandbummier's point that it feels like I've lost - specifically - my thumbs. Instant send it a key part of how I use DEVONthink! ( sad smiley emoji )